FOREST RAILROADS 291 
be built, engineers recommend the use of a transit in preliminary 
work, because of the accuracy demanded in final results. Some 
use a railroad compass and a hand level of the Abney type both 
for main lines and spurs. In a fairly level country the railroad 
compass will meet all needs, in fact some find a small staff com- 
pass ample. 
The engineer, having traveled over the proposed route one or 
more times and knowing the problems to be solved, locates a line 
of tangents and sets stakes marked with the station number, at 
100-foot intervals along the right-of-way. As the line pro- 
gresses, the engineer, by trial, selects the points which will keep 
his grades and curves within the limits set for the line. Several 
trial lines may be necessary to secure a satisfactory grade. 
On spur lines in a rough region and on main lines in a fairly 
level region, the preliminary survey is dispensed with. A rail- 
road compass or a box compass is often used in lieu of a transit, 
and in many sections the woods foreman or superintendent 
replaces the engineer. 
A common method in the pineries of the South is to locate a 
line of tangents by the use of three 6-foot straight pickets, along 
which the locator sights, placing center stakes at 100-foot in- 
tervals. 
The final location of the line of tangents is followed by the 
location of curves. Loggers have a number of rule-of-thumb 
methods of locating curves, which, although somewhat inaccurate, 
are satisfactory for railroads where a high degree of engineering 
ability is not demanded. Many who use rule-of-thumb methods 
determine the deflection angle by eye and lay off trial curves, 
persisting until they find one which will connect their two tan- 
gents. Several methods are in general use by logging engineers 
for laying out curves on logging roads, among them the tangent- 
offset method; offsets from chords produced, the field man using 
a table of offsets for a given degree of curvature; b}- computing 
in the office from a plotted traverse the offsets from stations on 
a line of tangents followed by field location; and by the use of 
a transit or compass to lay off stations on a curve by means of 
deflection angles. 
On main line work in a rough region, the location survey is 
followed by a line of levels which furnish data for a profile map 
on which the "elevation of grade" is shown. This is preliminary 
